This talk

• what, not why
• ask me in the hallway about why

Actyx

Needs at Actyx

• event storage for distributed event sourcing system
• partition tolerant
• local first
• first small private swarms
• then on global IPFS, so needs encryption

Requirements

• content-addressed
• append only log*
• indexed by offset, queriable by tags
• compressed
• encrypted

Append only log

• fast append
• events are addressed by stable index
• can remove data at index ranges, but index will remain

Querying

• data at index i
• index range i..j
• time range 2020-01-01..2020-02-01
• tags 'machine', 'order-1234'
• boolean combination of the above (& and |)

Banyan

Banyan

• rust crate

• MIT + Apache

• persistent sequence of (K,V) pairs

• fast access by index

• custom queries by summary

  • actyx uses tags and time, but you can define your own summary type

• deletion of ranges

• no arbitrary insertion and deletion

Types

• value type, always a CBOR blob
  • opaque CBOR, tag 42 links will be scraped before encryption
• key type Key
  • can be summarized, tag 42 links will be scraped
• symmary type Summary
  • summary is computed from keys or other summaries
• link type Link
  • can be a Cid, but does not have to
  • at Actyx, [u8;32] and fix the hash algo for entire trees

TreeTypes

TreeTypes groups all types used by a banyan family of trees, or Forest

pub trait TreeTypes {
    // type bounds simplified for readability
    type Key;
    type Summary;
    type Link: Cbor42;
    type KeySeq: Cbor42 + Summarizable<Self::Summary>;
    type SummarySeq: Cbor42 + Summarizable<Self::Summary>;
}

Block format as seen from ipfs

#[derive(DagCbor)]
struct Node(
    u64, // offset in the stream
    Vec<Cid>, // cids scraped from bytes
    Bytes, // compressed and encrypted CBOR42
);

Cbor42

• CBOR as described in RFC7049, plus tag 42 (Cids)
• why not dag-cbor?
  • I want CBOR, not binary JSON
  • dag-cbor allows only strings as dict keys
  • very limiting compared to CBOR
  • don’t care that much about canonicalization

Example

main.rs

• use banyan as just a sequence
• use banyan like actyx does
• use banyan with custom index